Imaging properties of lenses used in optical apparatus and systems can suffer from one or more optical aberrations, such as astigmatism, chromatic aberration, distortion, field curvature and spherical aberration. Optical aberrations can be mitigated through several techniques, including utilization of various structures in conjunction with the lens. In one technique, an external stop is positioned in front of the object side of a lens to assist in correcting off-axis aberrations. Moreover, additional lens structures can be used to correct optical aberrations of a first lens. Achromat doublets, for example, can be used to minimize chromatic aberration of a first lens.
While offering greater degrees of freedom for correcting optical aberrations, optical apparatus comprising compound lens arrangements and/or external stops demonstrate cost and fabrication disadvantages in comparison to optical apparatus based on single element (singlet) lens designs. The use of multiple lenses and/or external stops can increase manufacturing costs as multiple components are required for apparatus completion. Additionally, multiple lenses and/or external stops can increase manufacturing time as these components require accurate alignment and are subject to tight tolerances. Furthermore, a faulty lens or external stop or misalignment thereof can render the optical apparatus defective thereby increasing manufacturing inefficiencies.